1. Field of the Invention
This invention relates to textile yarn carriers. More particularly, this invention relates to tubes used for high speed winding of pre-oriented thermoplastic textile yarns. For the purposes of this invention, "pre-oriented yarns" are yarns of which the molecular orientation is not complete and which have a residual draw ratio wherein drawing is completed during a subsequent continuous or discontinuous process.
2. Technical Considerations and Prior Art
The process of spinning and partially drawing polyester yarns continuously is known. These yarns are wound in a pre-oriented state with a residual draw ratio which varies from 1.4 to 2. Drawing to a standard draw ratio (about 4) is completed, for example, during texturing.
However, one is faced with problems when winding pre-oriented yarns with a tangential drive onto winding packages with a winding roll. These problems are more pronounced at the beginning of the winding operation. The winding roll is designed to control the package winding speed, while completely or partly supplying the moment necessary for driving it. The winding roll is also provided with two over thicknesses which act as start-up rings and exhibit a 0.1 to 1 mm diameter in excess of the other parts of the winding roll. These rings are positioned on the winding roll at locations corresponding to the tube end areas and outside of the package winding area.
One purpose of the start-up rings is to confer an overspeed to the winding tube in order that, upon starting, the yarn winds up onto the tube rather than onto the winding roll. The tube is held by a device such as a stirrup provided with small discs holding it by its extremities, or by a spindle traversing its whole length and driving it in rotation. This last solution may be selected in high speed windings, that is, of 6,000 - 7,000 meters/minute or more.
The yarn is distributed along the tube by a traversing device. In spite of all of the precautions which are taken on building traversing devices, the yarn distribution is not strictly uniform along the entire length of the tube because there is an excess accumulation of material in the zone where the traversing devices reverse. In both the reversal zones at both ends of the tube, the yarn speed is not constant, but decreases, then is null, and after reversal, increases again up to its nominal value. The material accumulation at reversal points produces overthicknesses or "incipient projections". One purpose of the driving roll is to compress these projections in order that the winding package generatrix may be nearly rectilinear. When the winding up operation starts, the tube is in contact with the rings and the package does not touch the driving roll. However, the package grows and at both ends forms incipient projections which, at a given time, come into contact with the driving roll.
It has been observed that contact between package ends and the winding roll could prejudicially effect pre-oriented yarns in the following ways:
a. At the top of the projections, the yarn is oversped in relation to the winding roll. This overspeed depending on the dimensions of the driving roll and the winding package tube may be about 1.5%. For a winding speed of 3,000 m/min, this overspeed is about 45 m/min, which is not negligible. Therefore, when the projections come into contact with the driving roll, there is a slippage of 45 m/min which applies to short lengths of pre-oriented yarn.
b. When a cardboard tube is used as a winding package tube, its geometrical characteristics frequently vary. Consequently, the tube may exhibit faults due to inaccurate centering which, on rotation, produces vibrations which impact on the package on the winding roll.
When using a prior art tube, the pre-oriented yarn on contacting the winding roll is submitted to the above-cited effects a and b at the level of the incipient projections. It is subjected at these locations to strains which, at the reversal points, produce an impact which overdraws portions of the yarn about one centimeter long. Thus, after winding, this yarn exhibits length fractions of different molecular orientation which, on the last drawing operation (for example, on simultaneous draw-texturing) will produce under-drawn lengths. These under-drawn lengths produce faulty yarns with respect to count and dyeing, which are treated in an aleatory manner in commercial production, according to the quality of the winding tube used. This fault is currently referred to as "bobbin inner end fault".
It has been observed that when a tube is mounted on a spindle traversing its whole length, there is a point where the fault repeats itself more markedly with a periodicity corresponding to the reciprocating travel of the traversing guide. The more marked fault corresponds to the reversal point situated at the back part of the spindle (by "back" is meant the part of the spindle situated on the side of its fixation on the winder frame). The forepart of the spindle is far from the fixation and exhibits higher flexibility, thus allowing strains to be absorbed. Since the back part of the spindle is more rigid than the forepart, the yarn absorbs these strains, which causes deformation of the yarn.
To solve the problem of "bobbin inner end fault", reducing the pressure of the tube against the winding roll at the beginning of the winding operation was tried. Thus, a usual force of 40 to 50 N was reduced from 10 to 20 N during the first winding phase. Such a process, however, if it reduces faults, it does not eliminate faults totally.